CyclicBarrier in Java

CyclicBarrier in Java

CyclicBarrier lets a fixed number of threads wait until all participants reach the same synchronization point.

Real-World Use Cases

• phased simulation systems
• parallel data preparation before a final merge
• batch processing pipelines with step boundaries

How It Works

• create barrier with N parties
• each worker calls await()
• once all N arrive, optional barrier action runs
• barrier can be reused for next cycle

Java 8 Example

import java.util.concurrent.CyclicBarrier;

public class CyclicBarrierExample {
    public static void main(String[] args) {
        CyclicBarrier barrier = new CyclicBarrier(3, () ->
                System.out.println("All parties arrived. Merge step starts."));

        for (int i = 1; i <= 3; i++) {
            final int id = i;
            new Thread(() -> {
                try {
                    System.out.println("Worker " + id + " preparing data");
                    Thread.sleep(500L * id);
                    barrier.await();
                    System.out.println("Worker " + id + " continues next phase");
                } catch (Exception e) {
                    Thread.currentThread().interrupt();
                }
            }).start();
        }
    }
}

JDK 11 and Java 17 Notes

CyclicBarrier remains a stable and relevant choice in JDK 11 and Java 17 for repeated phase synchronization.

Java 21+ Guidance

For request-scoped parallel tasks, prefer StructuredTaskScope style orchestration over manual barriers when possible. Use CyclicBarrier when you explicitly need reusable phase synchronization.

Java 25 Note

No major usage change expected for CyclicBarrier; API is mature and stable.

Key Takeaways

• CyclicBarrier is for reusable phase coordination.
• Handle BrokenBarrierException and interruption correctly.
• Use it only when all participants are known upfront.